Unironically anonymous imageboards (not 4chan, 4chan is overcrowded at this point). Sure, you will get called names, but at least you won't get censored and/or downvoted into oblivion as it happens on Reddit (or HN) if you express opinion, that goes againt majority's belief. Your comment will be as visible as theirs. Another big advantage is complete anonymity - nobody knows anything about you, they only see the content of your post and nothing else.

I have had some of the best thought-provoking discussion about politics or life in general on anonymous imageboards.